This invention relates to a device, and in particular to a device comprising rollers, for applying fluid to a moving web.
Such a device is described in German patent document (Deutsche Patentschrift) Ser. No. 569,612. In that device, three rollers are disposed in a roller frame one above the other, the upper and the lower roller each having an elastic rubber covering and the middle roller having an engraved cylindrical surface. The upper and lower rollers are engageable with the middle roller at respective lines of contact or nips, the contact pressures at the nips being independently variable. A bottom portion of the lower roller is immersed during rotation thereof in a pool of liquid contained in a trough, the trough having a length equal to the width of a web passing through the upper roller slot or nip. The amount of fluid transferred to the web is controlled by varying the contact pressures at the nips and by changing the fineness of the grooves or notches engraved in the surface of the middle roller.
A device for applying liquid in small quantities to a fabric web is described in German patent document Ser. No. 197,893. This device likewise comprises a vertical array of rollers rotatable about respective parallel horizontal axes, the lowermost roller rotating in a trough extending the width of the fabric web. During rotation, the lowermost roller transfers fluid from its surface to a notched or engraved roller. Fluid sitting in the notches of this roller is removed by means of a brush roller and applied to a pair of fluid transfer rollers juxtaposed thereto, the fabric web being drawn past the transfer rollers. The transfer rollers can rotate at greater speeds than the engraved roller, the speed differential being taken up by motion relative to the brush roller. Because the two transfer rollers and the fabric web move more rapidly than the engraved roller, a determinate quantity of fluid can be distributed over a greater web length, whereby a small amount of fluid per unit of area is applicable.
Uniformity of fluid transfer is virtually unattainable in such a device, owing to the pressure by the brush and the circumstance that the fluid transfer rollers are engaged by the web only on one side, rather than at a roller nip. The brush undergoes a wear and tear which is difficult to control and which strongly influences the transfer relationships. In addition, there is no even distribution of fluid on the web, such a distribution being producable by a roller nip.
The object of this invention is to provide a three-roller device of the above-described type which can apply to a web, in a very uniform distribution, very small quantities of fluid per unit area.